Microstructure evolution and thermodynamic mechanisms in an oxide-dispersed Fe–Ni–Ti–Mo maraging steel

Laser powder bed fusion (LPBF) enables the fabrication of ultrahigh-strength steels with tailored microstructures through intrinsic thermal cycling. Here, an oxide-dispersed Fe–Ni–Ti–Mo maraging steel was produced by dielectrophoretically depositing Y2O3 nanoparticles onto feedstock powder. The as-printed alloy exhibits martensitic cellular grains with ~6 vol.% intercellular austenite films following the Kurdjumov–Sachs orientation. Aging at 480 °C for 3 h induces concurrent η-Ni3Ti precipitation and reverse austenite formation, increasing the austenite fraction to ~16%. A thermodynamic–mechanical framework combining regular-solution modeling, Scheil–Gulliver solidification, and Patel–Cohen analysis rationalizes phase evolution and TRIP behavior. Multiscale characterization validates interfacial crystallography and phase partitioning, while strength modeling reveals contributions from solution, dislocation, boundary, and precipitate strengthening. The oxide-modified alloy achieves superior yield strength–ductility synergy (as-printed: 863 MPa, 14.6%; aged: 1714 MPa, 5.3%) compared with the oxide-free counterpart, establishing a thermodynamics-guided design route for LPBF maraging steels.